Micro- and macrokinetic behavior of the subunit gating channel

Abstract

The concept of a channel that builds up from subunit molecules by way of aggregation can provide the framework for a unified description of electrical excitability in cell and model membranes at the micro- and macrokinetic level. Monte Carlo simulations of the microkinetics of a subunit channel predict two extreme kinds of gating behavior. Depending on the reaction parameters, a simulation can result either in single-step open-closed microkinetics, as elucuidated by noise analysis of excitable cell membranes, or in records resembling the multi-step conductance bursts that are measured in lipid bilayers modified by alamethicin. Numerical calculations of the voltage-clamp macrokinetics for the two cases reveal that the set of parameters that produces nerve- and muscle-like fluctuations gives Hodgkin-Huxley-type time courses, while the set that results in alamethicin-like fluctuation behavior gives alamethicin-like macrokinetics. The macrokinetic behavior is generated by summing microkinetic simulations for the nerve and the alamethicin case.